Limit the damage of a hacked sender acount

[Daniel Miller]

I had a couple of accounts with too simple passwords hacked. And obviously 
my mail server is entirely too efficient - I think about 50k spams got 
blasted out before I caught it (because we got in the DNSBL's).

Separate from improving the password security - what can I do to limit the 
damage a compromised account can cause? Without receiving user complaints 
about not being able to send the latest cute kitty pictures to their whole 
addressbook?

Are there per-sender limits that can/should be applied? And is there a way 
I can be notified of a suspicious condition - without manually monitoring 
the queue?

--
Daniel